The present invention relates to an apparatus for removing fine particles in an exhaust gas, which removes black smoke particles contained in exhaust gases emitted from diesel engines and various boilers, and an apparatus for cleaning an exhaust gas.
An exhaust gas from a diesel engine contains nitrogen oxides and black smoke particles (particulate) that are harmful to human bodies. Among them, the black smoke particles consist mainly of carbons. To remove the particles, various fine particle-removing devices have already been proposed. For example, JPA 01-77715 discloses such a device that employs a ceramic filter of cross-flow type. In this device, an intake path and an exhaust path for an exhaust gas are arranged in such a relation that they cross with each other at right angle via a partition of gas-permeable porous solid (ceramic). The black smoke particles are captured at the partition when the introduced exhaust gas penetrates through the partition.
JPA 01-159408, for example, also discloses a fine particle-removing device that utilizes a ceramic filter with a honeycomb structure. In this device, a gas-permeable porous solid is also used as partitions that form respective cells in the honeycomb structure. In addition, one end with respect to a first group of cells and the other end with respect to a second group of cells are closed. Then, an exhaust gas is introduced into the second group of cells from the first group of cells via respective partitions so as to capture the black smoke particles at each partition.
Either of the above-mentioned conventional devices for removing fine particles in exhaust gases is, however, a system for filtering the black smoke particles by allowing them to penetrate through the partition of a porous material. Accordingly, there is a disadvantage that a resistance against the exhaust gas flow is increased and the output of the diesel engine is lowered. In addition, the black smoke particles captured at the partition are finally burned up to dispose. At this moment, another disadvantage is caused because ashes remained after burning up may stay over the surface of the partition and clog the filter gradually, lowering the filter function finally, increasing the exhaust resistance further more and lowering the output of the engine. For this reason, adapted in the art is a method of rinsing back the black smoke particles captured at the surface of the ceramic partition and burning them up after transferring them to another location. Therefore, the device disadvantageously becomes a larger scale.
The present invention has been made in consideration of such the situations and has an object to provide an apparatus for removing fine particles in an exhaust gas. The apparatus is capable of suppressing an increase of an exhaust resistance so as to prevent the output from lowering, and of simplifying the apparatus by processing captured fine particles efficiently. The present invention also provides an apparatus for cleaning an exhaust gas that utilizes the apparatus for removing fine particles.
The present invention is provided with a fine particle-removing apparatus connected to an exhaust path for an exhaust gas emitted from a combustion engine, for removing fine particles contained in the exhaust gas. The apparatus comprises a filter for capturing the fine particles contained in the exhaust gas at partitions during the exhaust gas being introduced into one side and exhausted from the other side of a plurality of paths. The plurality of paths are defined by the partitions and formed to extend in the direction of a flow of the exhaust gas. The apparatus also comprises a fuel injection nozzle for injecting a fuel into an exhaust gas intake portion of the filter, and an ignition means for igniting the fuel injected from the fuel injection nozzle.
In the present invention, once the exhaust gas is introduced into each of the plurality of narrow paths that extend in the direction of the gas flow, the exhaust gas travels within the paths while the gas is disturbed to flow by the partitions that define the paths. In this process, the fine particles contained in the exhaust gas are captured at the surfaces of the partitions, which are in parallel to the direction in which the paths extend. The fuel is injected into the exhaust gas intake portion of the filter from the fuel injection nozzle. When the ignition means ignites the fuel, flames are carried by the exhaust gas flow and extend over each wall of the paths, burning up the fine particles captured at the walls of the paths. Ashes remained after burning are ejected to the outside of the filter in accordance with the exhaust gas flow.
As described above, according to the present invention, the filter forms a plurality of paths extending in the direction of the exhaust gas flow. Then, the exhaust gas is introduced into one side and emitted from the other side of the paths. In this process, the fine particles are captured at the walls of the paths. Therefore, the exhaust gas can flow extremely smoother and the exhaust resistance can be suppressed sufficiently lower than the conventional systems that filter the gas with porous materials, thereby preventing the output from lowering. The exhaust gas is disturbed slightly to flow during it travels through the narrow paths. As the result, the fine particles in the exhaust gas can be captured well at the partition walls of the paths. In addition, the ashes, which remains after burning the fine particles captured at the partition walls, are smoothly ejected to the outside of the filter and do not stay over the filter surfaces. Thus, maintenance is hardly required and the apparatus can be simplified. Further, if the same light oil as a fuel for the diesel engine is used as the fuel for burning the fine particles, for example, a particular fuel supply is not required and maintenance becomes much easier.
If the filter is made of gas-permeable porous solid, the exhaust gas, which travels along with turbulent flows in the narrow paths, flows so as to penetrate even into the inside of the partitions. Thus, the fine particles contained in the exhaust gas can be captured further effectively at the partition walls.
The filter may be definitely formed to have plural paths extending in the direction of the exhaust gas flow and arranged in the direction perpendicular to the exhaust gas flow. The plural paths are defined by plural partitions, which consist of porous ceramic plates and arranged in parallel, and have substantially rectangular cross sections. More preferably, the filter may include plural stages of filter units. In this case, porous ceramic partitions in adjacent filter units may be arranged to cross at right angle to each other. This arrangement enables to increase the effect of providing the exhaust gas with turbulent flows so as to capture the fine particles further effectively.
Further comprising a means for introducing a combustion promoting gas such as an air into the exhaust gas intake portion of the filter, as well as applying a combustion promoting agent on at least parts of the partition surfaces of the filter, may improve a combustion efficiency during the fine particles are burned.
Burning the fine particles may be performed intermittently when a predetermined amount of the particles is accumulated over the partition surfaces of the filter. In this case, the apparatus may perform a burning operation when a temperature of the filter drops to a predetermined value by further comprising a temperature sensor for detecting a temperature of the filter and a control means, for example. The control means allows the fuel injection nozzle to inject the fuel and the ignition means to perform an igniting operation if the temperature sensor detects a temperature lowered down to a first temperature. The control means also halts the fuel injection nozzle to inject the fuel if the temperature sensor detects a temperature elevated up to a second temperature higher than the first temperature.
In case where the above-mentioned filter is disposed in an exhaust path of a diesel engine, combining the filter with an exhaust gas return control device for returning the exhaust gas from the exhaust path to an intake path of the diesel engine can configure an exhaust gas cleaning apparatus. Thus configured apparatus can prevent the black smoke from returning into the intake portion of the engine and reduce NOx at the same time. Arranging a catalyzing device at the exhaust portion of the filter may further clean the exhaust gas effectively.